“The construction… required skilled carpenters, masons, large metal furnaces and metallurgists to cast the speculum mirror, chains, pulleys and secondary mirrors,” explains Alicia Parsons, daughter of the seventh Earl of Rosse and great-great-great-granddaughter of William Parsons, the third Earl of Rosse, who had the giant instrument built on the grounds of nearby Birr Castle. “The telescope became a source of pride for the community, and it was affectionately nicknamed ‘The Leviathan of Parsonstown’ by locals.”

The telescope was at the cutting edge of technology. William Parsons had developed new methods of using speculum—an alloy of copper and tin—and built machines near the Leviathan site to grind and polish the brittle metal into two huge mirrors for his new telescope. (Speculum can be highly polished but tarnishes quickly.)

Until the Leviathan was built, the largest telescope was a 49.5-inch-wide reflector (just over four feet across) built in England by 18^th-century astronomer William Herschel. Herschel discovered two moons of Saturn with that telescope, but it was difficult to use. The Leviathan was designed to overcome its limits.

This Telescope Offered Early Hints of Faraway Galaxies | HISTORY